The invention relates to a process and an apparatus for the discharge of solids which form during the gasification of finely dispersed, in particular solid fuels, particularly during coal gasification, the actual reactor for the production of synthesis gas having a bottom outlet for the slag and being housed within a pressure vessel and a water bath being provided underneath the reactor to collect the solids formed during the coal gasification, these solids being in the form of ash, slag and fly ash. The apparatus is designed so that the solids collected in the water bath are continuously removed and directed into at least two different lock hoppers and said solids accumulate in at least one lock hopper at any one time.
The production of synthesis gas from carbon-containing fuels generally incurs the formation of solids which have to be removed from the process. Examples include ash or slag. DE 3144266 A1 and EP 800569 B1 describe a process in which the ash and slag formed in a gasification system operated under pressure are collected in a water bath, also known as a quench zone. The particles of ash and slag are discharged in batches from the gasification system in a downwards direction via a lock hopper underneath the gasification system. For this, there are shut-off devices above and below the lock hopper to separate the lock hopper from the gasification system on the fluid side. While the lock hopper is being filled with slag, it is connected to the gasification apparatus. To empty the lock hopper when it is full of slag, the lock hopper is separated from the water bath by closing the upper shut-off devices and depressurised before the slag is discharged by opening the lower shut-off devices. After being emptied, the lock hopper is refilled with water and reconnected to the water bath. During slag discharge, the slag accumulates in the water bath.
EP 290087 B1 also describes a process for the removal of slag from an apparatus for the gasification of coal. In the described apparatus there is also a lock hopper underneath the pressure vessel which can be separated from the pressure vessel using valves. The slag is also discharged in batches. During the discharge, the slag is collected in a water bath, also known as a slag quench vessel. EP 290087 B1 states that separation by means of a valve and the accumulation of slag above the valve may lead to slag bridging directly across the valve. This bridging causes problems during operation when the lock hopper is reconnected to the pressure vessel. In EP 290087 B1 this bridging is solubilised by means of a gas bubble inside the lock hopper, this gas bubble being at a lower pressure than in the pressure vessel.
U.S. Pat. No. 6,755,980 B1 describes an apparatus for the removal of slag, said apparatus having an additional intermediate vessel between the pressure vessel and the lock hopper. Again, the slag is discharged in batches by means of valves above and below the lock hopper. During discharge of the slag collected in the lock hopper, the slag accumulating in the water bath is collected in the intermediate vessel. Again, bridging is described on the closed valve which may likewise lead to problems. Here, the danger of bridging is reduced by discharging a stream of water from the lock hopper.
The processes described are characterised by crucial disadvantages. Discharging the solids in batches by means of a lock hopper requires an intermediate vessel or additional capacity inside the pressure vessel to hold the amount of solids which accumulate during discharge. Emptying the lock hopper batchwise also puts a great strain on the apparatus connected to it. The apparatus connected to it must be designed for large amounts of solids discharged in batches and not for the much smaller average solids process stream. Furthermore, separating the lock hopper by means of valves leads to bridging on the valves and thus to problems in discharging the solids after reconnecting the lock hopper.
Therefore, the objective is to find a process and an apparatus for the discharge of solids formed during gasification, in particular during coal gasification, which obviate the need for an intermediate vessel or additional capacity inside the pressure vessel to hold the amount of solids which accumulate during discharge. The objective is also to increase the amount of solids discharged per hour without changing the dimensioning of the lock hoppers and the upstream/downstream equipment. At the same time, the objective is also to avoid blockages on the lock hopper valves and thus also maloperation.
The invention achieves this objective in the form of a process for the discharge of slag and ash from an apparatus for the gasification of fuels, the actual gas generator having a bottom outlet for solids and being housed within the pressure vessel, with a water bath underneath the gas generator to collect the solids formed in the gas generator, and the solids from the water bath being directed via a flow divider element and subsequent shut-off devices into at least two different lock hoppers, where they are reduced in pressure.
What is claimed, in particular, is a process for discharging solids from a gasification apparatus for the production of synthesis gas, in which the solids from the gasification apparatus are directed into a water bath positioned underneath the gas generator, said gasification apparatus having a bottom outlet for solids and being inside a pressure vessel,
the process being characterised in that                the solids stream or the solids suspension from the water bath housed within the pressure vessel is directed into two or more lock hoppers simultaneously or consecutively by means of a flow divider mechanism made up of a flow divider element and two or more subsequent shut-off devices, the lock hoppers being connected directly or indirectly to the pressure vessel via a flow divider element, and        the solids stream or the solids suspension from the water bath for collecting the solids formed in the gasifier is fed into the lock hopper or hoppers, where it is subsequently reduced in pressure.        
Synthesis gas can be produced, for example, by means of a coal gasification process. The coal gasification reaction takes place in a pressure vessel which contains the coal gasification reactor as well as fixtures for supplying the feedstocks and fixtures for discharging the synthesis gas and the solids formed. In a common embodiment the solids are removed from the reactor in a downwards direction, there first being apparatus connected to the bottom of the coal gasification reactor in descending order to separate the solids from the synthesis gas, and to cool and discharge the synthesis gas as well as an apparatus to collect the hot solids and ash particles. This is typically a water bath. The water bath is usually connected to two lock hoppers below it.
Devices for scrubbing, drying and removing the solids are attached to the downstream end of the lock hoppers. The two lock hoppers are alternately connected to and separated from the water bath by means of shut-off devices above the lock hoppers. While one lock hopper is in contact with the liquid in the water bath and being filled with solids, the second lock hopper is emptied. The solids are encouraged to settle out in the lock hopper by discharging a stream of liquid from the lock hopper which is connected. As soon as the second lock hopper has been emptied, it is filled with water and then reconnected to the pressure vessel. As soon as the first hopper has been filled to its maximum level, the stream of liquid to encourage the solids to settle out is no longer discharged from the first lock hopper but from the second.
In so doing, the solids stream is diverted to the second hopper and the first lock hopper can be separated from the pressure vessel by closing the valve, without it being affected by the solids, thus largely preventing the settlement of solids on the valve. This continuous alternate operation of the lock hoppers allows a higher solids throughput to be achieved without having to modify the upstream/downstream plant components as the amount of solids discharged when the lock hopper is emptied does not increase.